Three questions related to the virology of HIV associated disease will be addressed: 1.) Is virus infection in the nervous system limited to cells of macrophage lineage? 2.) Does the amount of virus and virus replication correlate with neurological disease? 3.) Are specific strains of virus (involving specific sequences) related by virus invasion of CNS and to neurovirulence? Macrophages and microglia are infected in brain and spinal cord, but questions persist whether astrocytes or other neural cells are infected at levels too low to detect with prior methods. Using in situ PCR, detection of single copies of DNA or cDNA should be possible and cells with reactions can be identified with cell specific markers. Different neurological diseases may or may not be correlated with number of cells infected, quantity of virus replication or virus proteins. Methods of virus quantitation will be compared (virus isolation, immunocytochemical staining of antigens, antigen measurement and PCR of HIV DNA and HIV transcripts). With PCR and RT/PCR virus HIV DNA and HIV transcripts will be quantitated in brain, spinal cord, dorsal root ganglia and peripheral nerves of autopsy tissue from patients neurologically evaluated before death. Tissues from 11 seropositive persons dying before AIDS and patients with AIDS without neurological disease, and patients with dementia, vacuolar myelopathy and sensory neuropathy will be studied. Regional quantitation in the preAIDS nervous system will also be done. To investigate the possible role of virus strains and neurotropism and neurovirulence, both the V3 domain of gp120 and U3-R region of the LTR will be studied. Segments will be obtained directly from brain by PCR to avoid selection of in vitro cultivation. Macrophage tropism determined by a V3 domain of gp120 appears essential but not sufficient for neurotropism and determinants of neurovirulence have not been studied. Neurovirulence will be assessed by examining sequence variations of segments obtained from brains of AIDS patients without dementia but with virus in brain and from patients with rapidly progressive dementia. Site of virus, importance of virus burden and molecular basis of neurotropism and neurovirulence as aspects of HIV- associated neurological diseases important in designing drug therapy and vaccines.